Totally new and not run on the trailer at all ?

They call that an AZZ KICKER !

And yes, that would cause the OP's issues...for sure.

That's cool but the Bravo3 kit is not available.

Not new, run fine on the trailer first, then drive to launch and fail on start up.

just a fyi,anything above idle rpm on the garden hose can cause the impeller to fail.

Dont ever take anything for granted .... the dealer tech could have Efed up because his IPhone rang or some **** . Ive literally strapped the boat down on the trailer ,and backed into the water almost over the transom , to find air leaks (water) . Pull the inlet hose off your pump and back into water , the water should flow freely out of the hose .
If not, you have a blockage . Ive seen the Hose from the Transom to the Pump collapse , because the outer hose was kinked .

Well, I don't think that is the issue because of the inconsistency and the fact that a fresh impeller picks up water properly when nothing else has changed.
But, enough experienced advice is saying to change that hose, what can I lose, minor expense and some time.

I assume the hose can be changed without removing the drive, would that be correct???

i was under the impression that the merc sea pumps are all the same rear housing and impellor regardless of drive (other than alpha)
and that the front snout/ mount/pulley was different based off the year of production

could be, but I went thru the menu on your link and says B3 product not available

Then why did you dis me...LOL.

It's worth a good shot. Stop the trailer running and see what happens.

The drive must be taken off to access the plastic insert that holds the hose to bell housing..

You keep saying bell housing ?? the hose goes from the connection on the inner transom plate to the sea pump, a bell housing is a large round object that bolts to the rear of the block and has two tabs that bolts to the inner transom plate to support the back of the engine :lolhit:

the part the drive bolts to is also called a bell housing.

You guys are talking about 2 different hoses.

Anyone give any credence to the air lock theory.
Open cooling is kinda like having a drain cock open on a lower rad hose, it will drain until a vacuum is created unless you have the rad cap open to let air in.

Could my cooling system be doing the same thing when it is out of the water......

the water hose should be dropping to the water pump,not gonna siphon back.
have any pics of the pump and water lines.

you have been told to remove the hose from the intake side of the water pump and then back the boat in the water and check for water running out of the hose.have you tried this yet?

LOL I thought it was a helmet :helmet:

The pump, hose and spigot on the transom are nearly level, the boat sits with the bow up slightly in my driveway, so it will likely drain.
I live in hill country and it will drain when towing as well.
I`ll get some pics when I have time.

if I kept wiping out impellers,,I would install a sea strainer and keep it filled and high enough to hold water to the pump.

Not yet, work gets it the way
Ran it fine on the hose last night though.

that may be doable.

hose is pressure to the pump,,now try that in a big tub and see if it will suck the water up.

I get that, but the issue is inconsistency.
Burned up the impeller Saturday morning parked in the same place. Boat had sat for 2 weeks.
Installed new impeller, changed nothing else, and it has worked perfect since.
The process of changing the impeller would release an air lock, I believe.

I think time to drain back is the issue, and or the movement and incline to allow it to drain.

I have been thru all the hose stuff numerous times and not found a fault.

A strainer or vent on the water pump inlet hose sounds like a fix to me.

An Airlock in a Stock mercruiser setup is very unlikely. Do you have any friends that do Automotive Evap work ? If yes they have a Smoke Machine to check for leaks .
Hook it to the pump Inlet Hose , tape the water pickups closed on the drive , then see if smoke comes out any connections, Especially where the neck bolts to the back of the transom plate.
. You have an air leak , or kinked hose .
I would pull the drive , replace the bell housing ( or Helmet ) hose to transom plate , and the transom to pump hose in the bilge . Then I would split them with a razor blade .
You might get a surprise ! Or you could keep on with the Air Lock Theory and keep replacing Impellers on the water.

Are you just throwing impellers in and NO NEW HOUSINGS and the other new parts that comes with the kit ? You need to do the whole kit. You should the black plastic housing impeller set up.

Also how hard are you cranking down the bolts at the black plastic housing ??? They require a 3 pass to 10 lbs ft only in a star pattern of tightness. Overtightening the bolts cracks the housing and will not pump water.

Next who's impeller and or kit are you using ???? How old are these - new off the shelf or been laying around for years ???

Next your inlet hose engine compartment side is too long and kinked ??? check that out as a water restriction to the impeller.

Bravo does it has have duel water pick up - if so when running on the hose you need to block off the water inlets of the front bullet.

If you are installing the whole kit for the impelling - housing - wear plate and one small o ring and one larger one, impeller are you using all the new parts in the kit ??? Also again who's kit is it ?? You need to do the whole kit its about 100 bucks.

Did you hook up your hoses back side of the impeller housing wrong ?

I do have access to a smoke machine and am familiar with how they work. Good suggestion.

Again, I get that, and may end up pulling the drive.

But, no one has explained why it does not f-up every time.

And, more importantly, why a new impeller fixes it every time.
With the new drive or the old drive.

Remember, it only burns up on the first startup, not after it has been running.
If it starts and pumps water it keeps on pumping water.

Sometimes I change the impellers only, if the housing has not been scored, sometimes I do the whole kit, always Merc parts.
Either way, it always picks up water and runs perfect until the next time the boat is laid up.
The inlet hose to the pump looks like oe parts, is wire reinforced and I have removed it more than once to push something thru and check for obstructions and found nothing.
The hoses are not reversed on the impeller housing.

I believe my new drive [ installed end of last season] is dual pick up, has holes in front of the bullet. My old drive did not.
I have had the same impeller issue with both drives.

My thought process still goes back to why does a new impeller or full kit fix it every time.
Why does it work fine for the weekend, once it picks up water.
Why does it only fail after towing or sitting on the trailer for awhile.
Why the same issue with 2 drives/transoms.

I sincerely appreciate all the help and feedback everyone has offered and I know it seems like I am refuting what people are suggesting.
But I have already done most of what has been suggested.

Other than not running it on the trailer between each replacement.

What have you got to lose ? Don't run it on the trailer and see how long it lasts.

Are you blocking off the nose cone pickups when on the hose with the new drive. I know you are saying that you are having the same same problem with the old drive as the new one. However, even though the result is the same in a burned up impeller, it could have been being caused by two differnt things. Air introduced at the transome assembly or at the nose cone will equal a burned up pump at some ponit in either case.

I would take SB's advice and stop running it on the hose until you install a t-flush kit. Your on water failures I think are just chance after the impeller has been damaged from running on the hose.

I got into the habit of running on the trailer as I had a few incidents at the launch, dead batteries, hose leaks etc.

I put a battery charger-conditioner on this boat and it`s plugged into 110 while parked, so the batteries should not be an issue.

Maybe I don`t need to start it on the hose, pre-launch..
But again, it has taken a crap on first start up in the water too.
But worth a try, not much to lose at this point.

Good points, I have not been plugging the lower ports on the new drive.
Theory wise, that could be part of the current issue, but it still pulls water instantly with a new impeller.

But, for good practice, I will plug them in the future when flushing.

What would be the correct way to do that, duct tape, small wood dowels...

I am going with the SB plan for the near future as well.

I use duct tape, but I am sure either way would work.

Breaking impeller blades off....doesnt seem like something that is caused by lack of water,unless they are old an rotten. I sounds like water combined with a weird pressure reversion is causing the blades to get ripped off. When I had water issues with fresh impellers, it would melt them.

I had a double impeller failure whilst boat was in the water. Here is how it went... I was idling into the inner harbor in Baltimore. I ran out of fuel (not proud of this) literally at the fuel dock. The fuel dock had already closed,even though it was like 5:00. I got my buddy to tow me about 1/8 mile to pier to tie up for the night. Morning came and we headed straight for the fuel dock. Fueled up,ran blowers fired up both engines,went about my business...next thing I know I have two overheat alarms screming at me. Shut them down,felt risers,they were hot. Pulled both pumps, and almost all blades were broken off of the impellers.

I feel the failure occured when I ran out of fuel, not afterwards. Is your engine rotating backwards when you shut it off?

I also had two transom housings that corroded and crushed the hose coming in from the helmet.

Now everything is new and the Hardin stainless pumps are kicking ass on my 496 mag ho's. Good luck.

This one...http://www.cpperformance.com/p-14544...rhaul-kit.aspx

If you install the "Tee" fitting in the water intake hose before the SWP, you won't have to worry about muffs or taping anything off.

Bought the fittings and hose to do that today.
This is an easy fix and will guarantee water gets to the pump no matter how long it has been sitting.

I also bought clear 1 1/4 reinforced hose for the transom to sea water pump, maybe I will be able to see water or at least know the condition of the hose in the future,
It will likely discolor though.

I also re-evaluated my air lock theory.
The cooling system is vented to the atmosphere thru the exhaust, unlike an automotive system which is mostly air tight.
The open system in the boat will drain, but not likely airlock

that clear hose is for pressure, not suction. your pump will suck it flat. use wire reinforced 1-1/4 wet exhaust hose.

$4.99 says that you have an air leak some where on the suction side of the pump. Pressure from the hose feeds the pump so the lack of suction is overcome. If system is already primed like after your on-water repair the water is sealing the vacuum leak enough to keep pumping. Supply hose or pump housing or??

Thanx for the tip, the hose I used is reinforced and more than adequate for the job.

I did end up taking the drive off, even though it is new, to double check the hose from the bell housing to the transom and it is in perfect condition and installed properly and not leaking.
I took the inlet hose from the transom to the pump off and checked the inside and it is in good condtion, you can see thru it and it is not coming apart on the inside.

I replaced the w/p inlet hose with new hose and put at tee in it .
I know this does not address whatever is causing my problem but it does allow me to flush the engine and prime the w/p if I need to.

Many people have said I have a leak in the suction side of the water pump, which makes perfect sense, but, I have not been able to find that leak with 2 different drives.

Also, as I said, if there was a leak there, why can I put a new impeller on it, and touch nothing else, and have the new impeller pull water right away.

One thing a local tech said I may have a thermostat that is not seating and allowing the block to completely drain leaving the impeller dry after storage.

I'll pull the housing and have a look.